A method for producing a bar for an ultra-high-strength titanium alloy fastener

Abstract

This invention discloses a method for preparing ultra-high strength titanium alloy fastener bars, comprising the following steps: 1. Melting raw materials to obtain an ingot; 2. Forging, rolling, and drawing the ingot sequentially to obtain a titanium alloy bar; 3. Performing solution aging treatment on the titanium alloy bar to obtain the ultra-high strength titanium alloy fastener bar. This invention proposes a method combining forging, rolling, drawing, and solution aging treatments to prepare ultra-high strength titanium alloy fastener bars with a tensile strength of not less than 1500 MPa and a double shear strength of not less than 830 MPa. The shear strength of the prepared ultra-high strength titanium alloy fastener bars is significantly higher than that of existing titanium alloys, exhibiting significant performance advantages in strength and shear properties. It can be used to manufacture advanced aerospace rivets, bolts, and other fasteners to meet the design requirements of high weight reduction, long service life, and high corrosion resistance for aircraft main load-bearing components.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material processing and forming technology, specifically relating to a method for preparing ultra-high strength titanium alloy fastener bars. Background Technology

[0002] Titanium and titanium alloys are the preferred materials for manufacturing aerospace fasteners due to their superior properties, including high specific strength, excellent corrosion resistance, non-magnetic properties, weldability, and wide temperature adaptability. Replacing most steel fasteners with those of lower specific strength with titanium alloy fasteners has resulted in significant weight reduction for aircraft. At the same strength level, titanium fasteners are 70% lighter than steel fasteners. Furthermore, titanium alloys exhibit superior fatigue strength and sensitivity to stress concentration compared to steel for similar applications, along with high corrosion resistance under various climatic conditions. Therefore, the application of titanium fasteners is crucial for aerospace equipment.

[0003] Since aerospace operations are often conducted at high speeds, the relative positional stability between two components connected by fasteners is often determined by the shear strength of the fasteners themselves. Therefore, shear performance has become an important performance indicator for fastener applications.

[0004] With the development of my country's aerospace industry and the continuous improvement of connection technologies used in new aircraft and spacecraft, new requirements have been placed on new fasteners. The development of ultra-high-strength titanium alloy fasteners with tensile strength of 1200-1500 MPa and shear strength ≥750 MPa is one of the future development trends. For example, SPS Aerospace Fasteners Group's Aerlite 180 bolts, manufactured using SPSTITANT M761 titanium alloy, have a tensile strength of up to 1240 MPa and a shear strength of up to 745 MPa, reaching the strength levels of many alloy steel and corrosion-resistant alloy fasteners, while reducing weight by 40%. Alcoa has developed Timetal 555 titanium alloy high-strength bolts, with a tensile strength of 1508 MPa, elongation of 9%, and double shear strength of 786 MPa after solution treatment and aging, but there are currently no reports of its practical application. In summary, the research on titanium alloys for aerospace fasteners has been basically completed for strength levels of 970MPa (Ti-64, TB3), 1100MPa (β-C, Ti-153), and 1250MPa (TB8). Currently, research on the application of ultra-high strength titanium alloy fasteners with even higher strength levels is underway.

[0005] Therefore, a method for preparing ultra-high strength titanium alloy fastener bars is needed. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for preparing ultra-high strength titanium alloy fastener bars. This method proposes to prepare ultra-high strength titanium alloy fastener bars with a tensile strength of not less than 1500 MPa and a double shear strength of not less than 830 MPa by combining forging, rolling, drawing, and solution aging treatment of titanium alloy ingots. The shear strength of the prepared ultra-high strength titanium alloy fastener bars is significantly higher than that of existing titanium alloys, exhibiting significant performance advantages in strength and shear properties. These bars can be used to manufacture advanced aerospace rivets, bolts, and other fasteners to meet the design requirements of high weight reduction, long service life, and high corrosion resistance for the main load-bearing components of my country's new aircraft.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing ultra-high strength titanium alloy fastener rods, characterized in that the method includes the following steps:

[0008] Step 1: Melt the raw materials to obtain ingots;

[0009] Step 2: The ingot obtained in Step 1 is successively processed by forging, rolling and drawing to obtain titanium alloy bars;

[0010] Step 3: Perform solution aging treatment on the titanium alloy rods obtained in Step 2 to obtain ultra-high strength titanium alloy fastener rods; the tensile strength of the ultra-high strength titanium alloy fastener rods is not less than 1500MPa, and the double shear strength is not less than 830MPa.

[0011] This invention involves melting raw materials to obtain ingots, then sequentially forging, rolling, and drawing the ingots to obtain titanium alloy bars. Finally, the titanium alloy bars are subjected to solution aging treatment to obtain ultra-high strength titanium alloy fastener bars with a tensile strength of not less than 1500 MPa and a double shear strength of not less than 830 MPa. The shear strength of the ultra-high strength titanium alloy fastener bars prepared is significantly higher than that of existing titanium alloys. Its strength and shear performance have obvious performance advantages and can be used to manufacture advanced aerospace rivets, bolts, and other fasteners to meet the design requirements of high weight reduction, long service life, and high corrosion resistance for the main load-bearing components of my country's new aircraft.

[0012] The above-mentioned method for preparing ultra-high strength titanium alloy fastener bars is characterized in that the forging in step two involves 4 to 6 stages of progressively decreasing temperature forging, with a forging temperature of 830℃ to 1150℃ and a temperature drop of 50℃ to 100℃ between stages, and a forging ratio of not less than 1.6 per stage. This invention, by controlling the forging parameters, utilizes the excellent deformation capacity of the β-phase body-centered cubic structure above the phase transformation point to perform large deformation processing, fully breaking down coarse grains. Simultaneously, it employs the principle of phase transformation recrystallization to refine the microstructure, achieving recrystallization refinement and equiaxed shaping of the billet.

[0013] The above-mentioned method for preparing ultra-high strength titanium alloy fastener bars is characterized in that the rolling temperature in step two is 800℃~820℃, and the deformation amount is 50%~60%. This invention controls the rolling parameters to achieve appropriate deformation below the phase transformation point, ensuring that recrystallization grain growth does not occur due to deformation heat while simultaneously breaking down the grains to form a two-phase microstructure.

[0014] The above-mentioned method for preparing ultra-high strength titanium alloy fastener bars is characterized in that the drawing temperature in step three is 750℃~770℃, and the deformation is 50%~70%. This invention achieves low-temperature drawing by controlling the drawing parameters, forming a certain residual stress, thereby improving performance and strength.

[0015] The above-mentioned method for preparing ultra-high strength titanium alloy fastener rods is characterized in that the ultra-high strength titanium alloy in step three is a Ti-Al-Mo-Cr-Nb-Zr series titanium alloy.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] 1. This invention proposes to prepare ultra-high strength titanium alloy bars for fasteners with a tensile strength of not less than 1500MPa and a double shear strength of not less than 830MPa by combining titanium alloy ingots through forging, rolling, drawing and solution aging treatment. The shear strength of the prepared ultra-high strength titanium alloy fastener bars is significantly higher than that of existing titanium alloys. Its strength and shear performance have obvious performance advantages and can be used to manufacture advanced aerospace rivets, bolts and other fasteners to meet the design requirements of high weight reduction, long service life and high corrosion resistance of the main load-bearing components of my country's new aircraft.

[0018] 2. This invention controls the forging parameters and utilizes the excellent deformation capacity of the β-phase body-centered cubic structure above the phase transformation point to perform large deformation processing, fully breaking down coarse grains. At the same time, it uses the principle of phase transformation recrystallization to refine the microstructure, achieving the recrystallization refinement and equiaxing of the billet.

[0019] 3. This invention controls the rolling parameters to deform appropriately below the phase transformation point, breaking the grains while ensuring that recrystallization grains do not grow due to deformation heat, thus forming a two-phase region structure. By controlling the drawing parameters, low-temperature drawing is achieved, forming a certain residual stress, which improves the performance and strength.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1This is a microstructure diagram of the ultra-high strength titanium alloy fastener bar prepared in Example 1 of the present invention.

[0022] Figure 2 The image shows the IPF (Intensity Per Frame) of the ultra-high strength titanium alloy fastener bar prepared in Example 1 of this invention. Detailed Implementation

[0023] Example 1

[0024] This embodiment includes the following steps:

[0025] Step 1: Prepare the raw materials according to the formula Ti-Al-Mo-Cr-Nb-Zr, and then melt the raw materials to obtain ingots;

[0026] Step 2: The ingot obtained in Step 1 is sequentially forged, rolled, and drawn to obtain titanium alloy bars. The forging is a four-stage, progressively decreasing temperature forging process, with forging temperatures of 1150℃, 1050℃, 950℃, and 850℃, and a forging ratio of not less than 1.6 per stage. The rolling temperature is 800℃, and the deformation is 50%. The drawing temperature is 750℃, and the deformation is 70%.

[0027] Step 3: Perform solution aging treatment on the titanium alloy rods obtained in Step 2 to obtain ultra-high strength titanium alloy fastener rods.

[0028] The ultra-high strength titanium alloy fastener rod prepared in this embodiment has a tensile strength of 1531 MPa and a double shear strength of 882 MPa, according to the test results.

[0029] Figure 1 This is a microstructure image of the ultra-high strength titanium alloy fastener bar prepared in this embodiment. Figure 2 The IPF diagram of the ultra-high strength titanium alloy fastener bar prepared in this embodiment is shown below. Figure 1 and Figure 2 As can be seen from the data, the microstructure of the ultra-high strength titanium alloy fastener bar prepared in this embodiment is a uniform and fine (α+β) two-phase structure.

[0030] Example 2

[0031] This embodiment includes the following steps:

[0032] Step 1: Prepare the raw materials according to the formula Ti-Al-Mo-Cr-Nb-Zr, and then melt the raw materials to obtain ingots;

[0033] Step 2: The ingot obtained in Step 1 is sequentially forged, rolled, and drawn to obtain titanium alloy bars. The forging is a six-stage, progressively decreasing temperature forging process, with forging temperatures of 1150℃, 1100℃, 1050℃, 950℃, 900℃, and 850℃, and a forging ratio of not less than 1.6 per stage. The rolling temperature is 820℃, and the deformation is 60%. The drawing temperature is 770℃, and the deformation is 50%.

[0034] Step 3: Perform solution aging treatment on the titanium alloy rods obtained in Step 2 to obtain ultra-high strength titanium alloy fastener rods.

[0035] The ultra-high strength titanium alloy fastener rod prepared in this embodiment has a tensile strength of 1516 MPa and a double shear strength of 843 MPa, according to the test results.

[0036] Example 3

[0037] This embodiment includes the following steps:

[0038] Step 1: Prepare the raw materials according to the formula Ti-Al-Mo-Cr-Nb-Zr, and then melt the raw materials to obtain ingots;

[0039] Step 2: The ingot obtained in Step 1 is sequentially processed through forging, rolling, and drawing to obtain titanium alloy bars. The forging is a five-stage, progressively decreasing temperature forging process, with forging temperatures of 1150℃, 1080℃, 980℃, 900℃, and 830℃, and a forging ratio of not less than 1.6 per stage. The rolling temperature is 810℃, and the deformation is 55%. The drawing temperature is 760℃, and the deformation is 60%.

[0040] Step 3: Perform solution aging treatment on the titanium alloy rods obtained in Step 2 to obtain ultra-high strength titanium alloy fastener rods.

[0041] The ultra-high strength titanium alloy fastener rod prepared in this embodiment has a tensile strength of 1542 MPa and a double shear strength of 851 MPa, according to the test results.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing ultra-high strength titanium alloy fastener bars, characterized in that, The method includes the following steps: Step 1: Melt the raw materials to obtain ingots; Step 2: The ingot obtained in Step 1 is sequentially processed through forging, rolling, and drawing to obtain titanium alloy bars. The forging process involves 4 to 6 passes with progressively decreasing temperatures, with a forging temperature of 830℃ to 1150℃ and a temperature drop of 50℃ to 100℃ between passes, and a forging ratio of not less than 1.6 per pass. The rolling temperature is 800℃ to 820℃, and the deformation is 50% to 60%. Step 3: Perform solution aging treatment on the titanium alloy rods obtained in Step 2 to obtain ultra-high strength titanium alloy fastener rods; the tensile strength of the ultra-high strength titanium alloy fastener rods is not less than 1500MPa, and the double shear strength is not less than 830MPa; the drawing temperature is 750℃~770℃, and the deformation is 50%~70%; the ultra-high strength titanium alloy is a Ti-Al-Mo-Cr-Nb-Zr series titanium alloy.

Images